Monthly Downloads: 92
Programming language: Haskell
License: BSD 3-clause "New" or "Revised" License
Tags: Web    
Latest version: v0.5.0.1

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postgres-websockets is a middleware that adds websockets capabilites on top of PostgreSQL's asynchronous notifications using LISTEN and NOTIFY commands. The project was largely inspired and originaly designed for use with PostgREST.

postgres-websockets allows you to:

  • Open websockets with multiple channels and exchange messages with the database asynchronously.
  • Send messages to that websocket so they become a NOTIFY command in a PostgreSQL database.
  • Receive messages sent to any database channel though a websocket.
  • Authorize the use of channels using a JWT issued by another service or by another PostgREST endpoint.
  • Authorize read-only, write-only, or read and write websockets.

Running the server

Quickstart using docker-compose

The docker-compose.yml present in the repository will start a PostgreSQL database alongside a postgres-websockets and a pg-recorder. To try it out you will need Docker installed and git to clone this repository.

git clone https://github.com/diogob/postgres-websockets.git
cd postgres-websockets
docker-compose up

Building from source

To build the project I recommend the use of Stack. You also need to have git installed to download the source code. Having installed stack the following commands should install postgres-websockets into your ~/.local/bin directory:

git clone https://github.com/diogob/postgres-websockets.git
cd postgres-websockets
stack setup
stack build

If you have any problems processing any Postgres related library on a Mac, try installing Postgres.app.

After the build you should be able to run the server using ~/.local/bin/postgres-websockets (you can add ~/.local/bin to your PATH variable):

To run the example bellow you will need a PostgreSQL server running on port 5432 of your localhost.

PGWS_DB_URI="postgres://localhost:5432/postgres" PGWS_JWT_SECRET="auwhfdnskjhewfi34uwehdlaehsfkuaeiskjnfduierhfsiweskjcnzeiluwhskdewishdnpwe" ~/.local/bin/postgres-websockets
postgres-websockets <version> / Connects websockets to PostgreSQL asynchronous notifications.
Listening on port 3000

You can also use the provided [sample-env](./sample-env) file to export the needed variables:

source sample-env && ~/.local/bin/postgres-websockets

After running the above command, open your browser on http://localhost:3000 to see an example of usage.

The sample config file provided in the sample.conf file comes with a jwt secret just for testing and is used in the sample client. You will find the complete sources for the example under the folder client-example.

Opening connections

To open a websocket connection to the server there are two possible request formats.

  1. Requesting a channel and giving a token

When you request access to a channel called chat the address of the websockets will look like:


When the token contains a "channel" claim, the value of that claim has precedence over the requested channel.

  1. Giving only the token

When you inform only the token on the websocket address, the channel must be present in the claims of your token. The address will look like:


To use a secure socket (wss://) you will need a proxy server like nginx to handle the TLS layer. Some services (e.g. Heroku) will handle this automatially.

Receiving messages from the browser

Every message received from the browser will be in JSON format as:

  "claims": { "message_delivered_at": 0.0, "a_custom_claim_from_the_jwt": "your_custom_value" },
  "channel": "destination_channel",
  "payload": "message content"

Where claims contain any custom claims added to the JWT with the added message_delivered_at which marks the timestamp in unix format of when the message was processed by postgres-websockets just before being sent to the database. Also channel contains the channel requested in the JWT, and this should be used to send any messages back to that particular client. Finally payload contain a string with the message contents.

A easy way to process messages received asynchronously is to use pg-recorder with some custom stored procedures. For more options on notification processing check the PostgREST documentation on the topic.

Sending messages to the browser

To send a message to a particular channel on the browser one should notify the postgres-websockets listener channel and pass a JSON object containing the channel and payload such as:

SELECT pg_notify(
  json_build_object('channel', 'chat', 'payload', 'test')::text

Where postgres-websockets-listener is the database channel used by your instance of postgres-websockets and chat is the channel where the browser is connected (the same issued in the JWT used to connect).